Stock based Compensation (Details Textuals) (USD $)	12 Months Ended
Dec. 31, 2011 years	Dec. 31, 2010	Dec. 31, 2009
Stock based Compensation [Abstract]
Stock-based compensation expense	$ 12,400,000	$ 13,600,000	$ 16,000,000
Total tax benefit recognized in earnings from stock-based compensation	4,400,000	4,800,000	5,500,000
Unrecognized compensation expense related to unvested options and restricted stock awards	25,700,000
Total unrecognized compensation cost recognized over a weighted-average period	3.0
Stock based compensation expense expected to be recognized in 2012	80,000
Chairman Of Board Fully Vested Common Stock Compensation	200,000
Aggregate intrinsic value of options exercised	5,900,000	8,700,000	6,400,000
Cash receipts from option exercises	39,800,000	29,900,000	19,300,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	4,000,000
Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Reserved For Issuance	3,800,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	7,800,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value	$ 1,100,000

Chairman Of Board Fully Vested Common Stock Compensation

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Stock based compensation expense expected to be recognized in 2012, including the amortization of deferred policy acquistion costs, for all stock-based awards outstanding at December 31, 2011.

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Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant

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- Definition

The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation and including the effect of deferral and amortization of policy acquisition costs realated to stock-based compensation for our underwriters.

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Aggregate proceeds received by the entity during the annual period from exercises of stock or unit options and conversion of similar instruments granted under equity-based payment arrangements.

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As of the balance sheet date, the aggregate unrecognized cost of equity-based awards made to employees under equity-based compensation awards that have yet to vest.

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The weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, using a decimal to express in number of years.

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- Definition

The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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The total fair value of equity-based awards for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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The total accumulated difference between fair values of underlying shares on dates of exercise and exercise price on options which were exercised (or share units converted) into shares during the reporting period under the plan.

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